Infusion devices are typically used to deliver an infusion medium, such as a medication, to a patient. Implantable infusion devices are designed to be implanted in a patient's body to administer an infusion medium to the patient at a regulated dosage, over a period of time. External infusion devices may be designed to be portable, for example, to be worn outside of the patient's body and connected to the patient by a catheter. Other forms of infusion devices are non-portable devices, typically for use in a controlled environment, such as a hospital.
Electromagnetic pump mechanisms (e.g., mechanisms that include a coil and an actuator which moves relative thereto) are used in infusion devices to selectively drive infusion medium, for example, to a patient. Various forms of electromagnetic pumps have been developed for use in infusion devices operating in external or implant environments. For example, one or more various electromagnetic pump mechanisms are described in U.S. Pat. No. 4,594,058 issued 10 Jun. 1986 to Fischell, entitled “Single valve diaphragm pump with decreased sensitivity to ambient conditions”; U.S. Pat. No. 4,684,368 issued 4 Aug. 1987 to Kenyon, entitled “Inverted pump”; U.S. Pat. No. 4,569,641 issued 11 Feb. 1986 to Falk et al., entitled “Low power electromagnetic pump”; U.S. Pat. No. 4,568,250 issued 4 Feb. 1986 to Falk et al., entitled “Low power electromagnetic pump”; U.S. Pat. No. 4,636,150 issued 13 Jan. 1987 to Falk et al., entitled “Low power electromagnetic pump”; U.S. Pat. No. 4,714,234 issued 22 Dec. 1987 to Falk et al., entitled “Low power electromagnetic valve”; U.S. Pat. No. 6,595,756 B2 issued 22 Jul. 2003 to Gray et al., entitled “Electronic control system and process for electromagnetic pump”; U.S. Pat. No. 6,997,921 B2 issued 14 Feb. 2006 to Gray et al., entitled “Infusion device and driving mechanism for same”; U.S. Pat. No. 7,186,236 B2 issued 6 Mar. 2007 to Gibson et al., entitled “Infusion device and inlet structure for same”; U.S. Pat. No. 6,805,693 B2 issued 19 Oct. 2004 to Gray et al., entitled “Infusion device and driving mechanism for same”; and U.S. Pat. No. 6,652,510 B2 issued 25 Nov. 2003 to Lord et al., entitled “Implantable infusion device and reservoir for same.”
Typically, electromagnetic pump configurations, such as those described in the above-referenced patents, employ a conductive coil of the pump coupled to a power source using control electronics. The coil is selectively energized by the power source and control electronics (e.g., using a controller and a switch) to create an electromagnetic field which operates on a moveable actuator (e.g., armature and piston). When the coil is energized, the electromagnetic field causes the actuator to move, for example, against the force of a spring, toward a stroke position. When the coil is then de-energized, the spring force, for example, returns the actuator to the position it had prior to energizing the coil. By moving the actuator between the energized stroke position and its return position, a pumping action is accomplished by the electromagnetic pump.
In many circumstances, such as when electromagnetic pumps are used in infusion devices, the electromagnetic pumps may be operable for extended periods of time with a limited power supply. For example, battery-powered infusion devices may be implanted in or otherwise connected to patients to deliver medication at controlled intervals over a prolonged period of time. As battery power supplies have limited capacities, such devices may require multiple replacements of batteries over their operational life. In the case of an electromagnetic pump used in an implanted infusion device, a replacement of a battery may require the surgical removal of the infusion device. Even with external devices, the replacement of a battery may require specialized tools, parts, or skills which necessitate the services of a specialist or trained technician. As such, in the art of electromagnetic pumps, for example, that are used in infusion devices, there is a desire to make efficient use of the power supply.
In many prior infusion devices, capacitor discharge power control circuits are used as the power source for the electromagnetic pump. Generally, such power control circuits include a capacitor that is charged by a battery and selectively discharged to the coil of the electromagnetic pump to power the pump operation. For example, each discharge of the capacitor delivers an electrical power pulse to the coil sufficient to energize the coil and cause the pump to make one complete stroke. The capacitor is charged by the battery between pump strokes.
To operate the electromagnetic pump under generally all expected power load conditions, the capacitor size of the power control circuits is generally selected such that the power output per complete discharge is sufficient to operate the pump in the greatest expected power load condition. As a result, sufficient power to operate the pump in the greatest expected load condition is provided to the pump, even when the pump is not operating under the greatest expected load. Such a complete power discharge at every pump stroke, independent of the pump's power needs, results in a waste of electrical power.
Various manners of attempting to decrease power consumption have been attempted. For example, generally, control signal circuitry is programmed or configured to generate a signal to control the closure of a switch coupling the power source to the electromagnetic pump upon the occurrence of one or more various events. For example, such events may include the expiration of a predetermined time period after initiation of a stroke and prior to initiation of a subsequent stroke. However, even prior to the expiration of a predetermined time period, end of stroke of the electromagnetic pump generally occurs. Allowing discharge of the capacitor (e.g., application of power to the electromagnetic pump) through expiration of the predetermined time period even when end of stroke has occurred would be an expenditure of unnecessary power.
As such, various techniques have been described for use in controlling the capacitor discharge to the electromagnetic pump to reduce power consumption. For example, in U.S. Pat. No. 6,595,756 to Gray et al., a detector for detecting the end of a pump stroke is described such that a power control circuit may cut off power to the pump coil prior to the detected end of the pump stroke. As described therein, for example, the back electromotive force (back EMF) of the coil is detected to determine when or where the actuator is capable of completing its full stroke motion after the capacitor discharge is cut off. By detecting or monitoring the back EMF generated in the coil, a suitable cut off time may be determined. Further, as described therein, a sharp positive rise or a change in direction of a coil current can indicate actuator deceleration that occurs at the actual end of the actuator's forward stroke. A suitable capacitor cut off point can also be selected based thereon.